Following the fast progress and development of technology, many machining techniques with high precision are developed, such as the technique of electrical discharge machining (EDM) which the material is removed by the erosive action of electrical discharges (sparks) provided by a generator. The same phenomenon of EDM is applied at the micron level for micromachining. The process is called as micro-EDM. In general, in the conventional micro-EDM process, there is an unavoidable offset between the electrode center A and the machining center B. Therefore, the phenomena of hole enlargement or eccentric circle will happen since the electrode C is working off-centered during the machining process as shown in FIG. 1A. In order to overcome the aforementioned problem, some manufacturers perform a refinishing work to the electrode C after the electrode C is securely clamped so as to eliminate the unavoidable eccentric occurred during the clamping. The refinishing work is shown in FIG. 1B, and is addressed as “Electrical Discharge Grinding”.
Currently, there are two micro-EDM processes being used for fabricating a microelectrode, namely, the electrical discharge machining of column electrode as shown in FIG. 2, and wire-cut electrical discharge machining as shown in FIG. 3. However, there are pros and cons of the two conventional methods, and the drawback of the former is that it is impossible to repetitiously compensate the wear and tear of the column electrode generated in the discharge machining process, and the shortcoming of the latter is that the two wire guides E are too widely arranged and cause an unstable movement of the wire electrode. Both shortcomings result in the decreasing of machining precision.
FIG. 4 shows the basic features of a conventional wire-cut EDM (WEDM) machine. The electrode G is a thin wire and it is pulled in constant tension and low speed through the workpiece H from a supply spool onto a take up mechanism. On application of a proper voltage, discharge occurs between the wire electrode and the workpiece. Brass wire is most commonly used for wire cutting that the machining is similar to the band saw machine. The wire electrode G should have sufficient tensile strength, toughness, and high conductivity, but usually can be used only once.
The conventional wire electrical discharge grinding applies the principle of the foregoing WEDM. As seen in FIG. 5, a brass wire I is used as the tool electrode and is connected to the cathode for processing an work piece, that is the anode electrode J. The grinding method is designed to maintain a gap between the tool and the workpiece in order to ensure electric-discharge between them, and new discharging surface of the brass wire I is in constant supply by the continuing movement of the brass wire I within the rail K in a constant speed. The length and diameter of the electrode J are entirely dependent on the position of the wire rail, so the electrode J may machine to the required micro dimension.
An improvement shown in FIG. 5 is the design of the wire guide K for replacing the wire guides of FIG. 3. Since the brass wire I is continuously and slowly moved in the wire rail K and is supported and restricted by the same, there is less swing of the brass wire during machining and thus a higher machining precision may be obtained. However, the design is restricted by the diameter of the wire, and the machined shape is also limited to cylindrical shape only that can not be used to machine a non-cylindrical-shaped electrode. In addition, the dimension of the brass wire acted as the wire electrode is restricted, that is, the thinner the brass wire is, the more difficult it will be for machining.